Evolving the language-ready brain and the social mechanisms that support language.

UNLABELLED: We first review the mirror-system hypothesis on the evolution of the language-ready brain, stressing the important role of imitation and protosign in providing the scaffolding for protospeech. We then assess the role of social interaction and non-specific knowledge of language in the emergence of new sign languages in deaf communities (focusing on Nicaraguan Sign Language). LEARNING OUTCOMES: (1) Readers will understand the difference between mirror systems in humans and monkeys, and see how the evolution of imitation and protosign required the biological evolution of mirror systems with linkages to diverse regions beyond the mirror system. (2) Readers will see how social structure complements brain mechanisms in yielding language through cultural evolution supported by having language-ready brains, rather than through possession of an innate Universal Grammar. (3) Readers will understand that ontogeny does not recapitulate phylogeny, but will appreciate what mechanisms currently operative in modern children acquiring language may also have served early humans during the cumulative invention of the idea of language.